1. Field of the Invention
This invention relates to an apparatus designed to assist a person having a foot-drop type of disability.
Persons who have sustained a stroke or suffer from diseases such as multiple sclerosis, post-polio sequelae, et al., generally incur certain neuromuscular pathological conditions because of damage to the nerves which innervate the muscles involved. This damage occurs centrally in the brain and/or spinal cord, or locally to peripheral nerves, such as those found in the leg, resulting in paralysis or partial paralysis in varying degrees of severity to different parts of the body. Generally, the distal joints are proportionately weaker than the more proximal joints (proximal meaning close to the midpoint of the body). Therefore, hip and knee extension (straightening) muscles while weakened with, for instance, a one-sided paralysis (commonly occuring in stroke victims), are, nevertheless, usually adequate to support the body by maintaining hip and knee extension sufficient for a limited amount of standing and walking which is usually feasible because the second leg is normal, and the person most often will have the added support and balance provided by a cane. As a result, a joint such as the ankle is frequently wholly or partially debilitated while the hip and/or knee remain relatively less affected.
Paralysis, in any degree, of the ankle and the mid-tarsal joint (just distal to the ankle), commonly known as foot-drop, present greater problems because of the independent movement required of them in walking. Ankle motions are dorsi-flexion (up) and plantar flexion (down), and mid-tarsal joint motions are inversion (inward turning) and eversion (outside edge of the foot turned up). Paralysis or partial paralysis for any of the reasons described herein usually impair the ankle and mid-tarsal joint such that dorsi-flexion and eversion are weaker than plantar flexion and inversion. Both dorsi-flexion and eversion, however, are required for walking so that the foot and toes do not drag. Therefore, a need exists for a foot-assist mechanism which selectively provides support for the foot by compensating for the affected muscles while allowing the functioning muscles or portions thereof to continue to operate to their fullest extent.
2. The Prior Art
A number of devices have been provided to date to alleviate foot-drop which includes short-leg braces having metal uprights, metal stirrups, molded calf cups, etc. These devices suffer disadvantages such as their weight, which taxes the strength of the leg, and their bulkiness, which tends to cause injury to the opposite ankle. More recently, U.S. Pat. No. 3,986,501 to Schad shows a foot-drop apparatus having a rigid vertical member curved and arched to conform to the rear of the calf of the human leg (the bottom of the vertical member having a cup-like shape to conform to the heel of the foot without extending under the heel) and a V-strap member connected at the top of the vertical member for the purpose of insertion at the shoe near the dorsum portion of the foot for lifting the dorsum of the foot when the heel is raised.
All of the above devices, however, are static in nature in that they maintain the foot in a relatively fixed position in relation to the leg (which is never greater than 90.degree.) at all times so that the entire lower leg from calf to toes moves en masse as a rigid structure being propelled and supported by the person's knee, hip and spine, thereby producing an awkward gait. Since the muscles involved in plantar flexion or straightening the ankle (the extreme of which is standing on the toes) are relatively much less affected in the disabilities described above, these devices actually immobilize working muscles to a degree, thereby causing their atrophy or earlier degeneration.
Also, the devices incorporating rigid members such as the device shown in the Schad '501 patent lose conformity with the wearer's leg due to muscle atrophy, slide up and down and/or rub against the leg, and cause excessive perspiration thus contributing to the discomfort of the wearer. Moreover, such irritation to the lower extremity of a person, who may have experienced some loss of sensory perception in the leg as a concomitant result of the debilitating condition, is likely to cause more severe discomfitures such as blistering, decubitus ulcers, etc.
It is, therefore, an object of the present invention to assist a person having a foot-drop type disability by providing a device which will aid the functioning of those muscles directly effected by a disabling condition, such as those described hereinbefore, but which allows full range of motion of the foot and usage of those muscles either not effected or only partially effected.
Commensurately, it is an object of this invention to provide a foot-drop assist apparatus which eliminates the discomfiture described above relating to static type foot-drop assist devices and the periodic adjusting or replacement normally associated with such devices.
Finally, it is intended to provide a foot-drop assist apparatus which is lightweight, relatively inconspicuous, easy to use, and very inexpensive to make and maintain.